1. Field of the Invention
The present invention relates to an optical beam spatial pattern recording device capable of measuring temporal changes in a spatial pattern of an optical beam.
2. Description of Related Art
A synchrotron device repeatedly emits optical beam pulses with an ultra-short pulse width at a high repetition rate. In order to analyze this emission, it is necessary to measure not only temporal changes in intensity of the optical beam pulses but also temporal changes in a spatial pattern or profile of each optical beam pulse.
Conventionally, a streak camera is used to measure the temporal changes in the intensity of the optical beam pulses. In order to measure the spatial pattern of each optical beam pulse, a spatial pattern measuring device, such as a gating image amplifier tube, a high speed video pick up device, a framing camera, and the like is used.
The above-described spatial pattern measuring devices, however, have various problems. The gating image amplifier tube can pick up data only at a specific instance. The gating image amplifier tube may not obtain data continuously. Data pick up interval, at which the high speed video pick up device repeatedly picks up data, is too long to measure the ultra-short pulse width of the synchrotron radiation. The data pick up interval, at which the framing camera picks up data, can be sufficiently short. However, the framing camera can continuously pick up only as small as thirty images.
When using both the streak camera and one of the spatial pattern measuring devices, a special optical system has to be used for each of the streak camera and the spatial pattern measuring device. That is, two different optical systems, connected to the streak camera and the spatial pattern measuring device, are provided to divide the optical beam into two beams and then to guide them to the respective devices. Alternatively, when measuring temporal change in intensity of the optical beam, the optical system for the streak camera is provided to guide the optical beam to the streak camera. When measuring the spatial pattern of the optical beam, the optical system is replaced with another optical system for guiding the optical beam to the spatial pattern measuring device. The entire device becomes complicated. It is difficult to perform an accurate adjustment.
In order to solve the above-described problems, Japanese Patent Publication No.4-38304 discloses a streak camera of a type which can measure also the spatial pattern of each optical beam pulse. This streak camera can obtain a sufficient amount of data desired to be obtained, and can repeatedly pick up data at a sufficiently short time interval. This streak camera is of a double sweeping type in which two pairs of deflection electrodes are provided for deflecting photoelectrons in two directions which are perpendicular to each other. In this streak tube, voltages of sawtooth waves are applied both to the two pairs of deflection electrodes. Measurement is performed while voltages of sawtooth waves are switchingly applied to the two pairs of deflection electrodes.
A streak tube, employed in this streak camera, is an electron tube in which the two pairs of deflection electrodes are located between a photoelectric conversion portion and a photoelectron detection portion.
With this streak tube, the spatial pattern of each optical beam pulse is detected as described below.
When optical beam pulses fall incident on the photoelectric conversion portion of the streak tube, the photoelectric conversion portion emits photoelectrons in correspondence with the incident optical beam pulses. As a result, photoelectron pulses are generated. A pair of horizontal deflection electrode plates and a pair of vertical deflection electrode plates are supplied with electric voltages and generate electric fields on the passage of the photoelectron pulses from the photoelectric conversion portion to the photoelectron detection portion. As a result, the traveling path of the photoelectron pulses is bent. More specifically, the pair of vertical deflection electrode plates bend the traveling path of the photoelectron pulses in a first direction (vertical direction), and the pair of horizontal deflection electrode plates bend the traveling path of the photoelectron pulses in a second direction (horizontal direction) which is perpendicular to the first direction. Voltages of sawtooth waves are applied between the two pairs of the deflection electrode plates in synchronization with the inputted optical beam pulses.